The present disclosure relates to solid-state imaging element, a method of manufacturing the same, a solid-state imaging apparatus, and an imaging apparatus. Specifically, the present disclosure relates to a solid-state imaging element capable of suppressing the generation of a dark current, a method of manufacturing the same, and a solid-state imaging apparatus and an imaging apparatus using such a solid-state imaging element.
In related art, in a video camera, a digital camera or the like, a solid-state imaging apparatus including a CCD (Charge Coupled Device) or a CMOS image sensor is widely used. In addition, in a CMOS type solid-state imaging apparatus, a surface irradiation type shown in FIG. 20 and a back irradiation type shown in FIG. 21 are used.
As shown in a schematic configuration diagram of FIG. 20, a surface irradiation type solid-state imaging apparatus 111 is configured to have a pixel region 113 in which a plurality of photodiodes PD becoming photoelectric conversion portions and a plurality of unit pixels 116 including a plurality of pixel transistors are formed on a semiconductor substrate 112. Although it is not shown, the pixel transistor shows a gate electrode 114 in FIG. 20 and schematically shows the existence of the pixel transistor.
Each photodiode PD is divided by an element separation region 115 formed of an impurity diffusion layer, and a multilayer wiring layer 119, on which a plurality of wirings 118 is disposed via an inter-layer insulation film 117, is formed on a surface side of the semiconductor substrate 112 formed with the pixel transistor. The wirings 118 are formed except for a portion corresponding to the position of the photodiode PD.
On the multilayer wiring layer 119, an on-chip color filter 121 and an on-chip micro lens 122 are sequentially formed via a planarization film 120. The on-chip color filter 121 is configured, for example, by arranging each color filter of red (R), green (G), and blue (B).
In the surface irradiation type solid-state imaging apparatus 111, light L is incident from the substrate surface side by using the substrate surface formed with the multilayer wiring layer 119 as a light reception surface 123.
Meanwhile, as shown in a schematic configuration diagram of FIG. 21, the back irradiation type solid-state imaging apparatus 131 is configured to have the pixel region 113 on which a plurality of photodiodes PD becoming the photoelectric conversion portions and the plurality of unit pixels 116 including the plurality of pixel transistors are formed on the semiconductor substrate 112. Although it is not shown, the pixel transistor is formed on the substrate surface side, shows the gate electrode 114 in FIG. 21, and schematically shows the existence of the pixel transistor.
Each photodiode PD is divided by the element separation region 115 formed of the impurity diffusion layer, and the multilayer wiring layer 119, on which a plurality of wirings 118 is disposed via an inter-layer insulation film 117, is formed on a surface side formed with the pixel transistor of the semiconductor substrate 112. In the back irradiation type, the wirings 118 can be formed regardless of the position of the photodiode PD.
Furthermore, on the back of the semiconductor substrate 112 which the photodiode PD faces, an insulation layer 128, an on-chip color filter 121, and an on-chip micro lens 122 are sequentially formed.
In the back irradiation type solid-state imaging apparatus 131, a substrate back of an opposite side of the substrate surface formed with the multilayer wiring layer and the pixel transistor is used as a light reception surface 132, and the light L is incident from the substrate back side. In addition, the light L is incident into the photodiode PD without being constrained by the multilayer wiring layer 119, and thus an opening of the photodiode PD can be expanded and high sensitivity is realized.
Incidentally, in the solid-state imaging apparatus as mentioned above, it is extremely important to promote an improvement in sensitivity and a reduction in noise. In particular, in the state in which an incident light does not exist, the dark current becoming a generation source of an interface state in an interface between the semiconductor substrate provided with a light reception portion performing the photoelectric conversion and an upper layer film is a noise to be reduced as the solid-state imaging apparatus.
Herein, the dark current is a phenomenon in which electrons are created from the photodiode PD and the periphery thereof even in the state where light is not incident to the light reception portion. When a large amount of the dark current is generated, a dark level becoming a standard of imaging capability of the solid-state imaging element deteriorates, whereby it is difficult to obtain resolution of a sufficient gray scale, and the sensitivity during imaging declines.
Furthermore, the interface state is an energy state in which electrons can exist due to a crystal defect in the semiconductor substrate or impurity, a bonding defect with an oxide film interface. When the interface state is increased, the generation of dark current is encouraged.
In addition, a factor of the interface state includes damage to the interface layer that is generated because oxygen atoms (O) are removed from the interface between the surface of the semiconductor substrate provided with the light reception portion performing the photoelectric conversion and the oxide film covering the same.
Hereinafter, this will be described using the drawings.
FIG. 22 is a schematic diagram that shows a structure of a back irradiation type solid-state imaging apparatus. The apparatus has a semiconductor substrate (Si substrate) 201 provided with a light reception portion (not shown) and an oxide film (SiO) 202 formed on the semiconductor substrate surface. Furthermore, a reflection preventing film (SiON) 203 is provided on the upper layer of the oxide film 202, an insulation film (SiO2) 204 is provided on the upper layer thereof, and a light shielding film (W) 206 is provided on a further upper layer of the insulation film 204 via an adhesion layer (Ti) 205.
Herein, the adhesion layer (Ti) 205 is formed so as to promote an improvement in adhesion between the light shielding film (W) 206 and the insulation film (SiO2) 204, but Ti has strong bonding strength with oxygen (O). Moreover, the oxygen atom (O) is removed from the interface between the oxide film 202 and the semiconductor substrate 201 by a reduction action due to Ti, whereby, as mentioned above, damage is generated in the interface between the oxide film 202 and the semiconductor substrate 201, and consequently, the generation of dark current is encouraged.
Incidentally, one technique for reducing the dark current is a method of hydrogen-terminating an uncombined hand of Si due to defect by heat-treating the bonding defect becoming the cause of the interface state in a hydrogen atmosphere (sintering).
However, in a region covered with the light shielding film, it may be hard to obtain an effect of hydrogen sinter processing, and it is difficult to sufficiently reduce the occurrence of interface state only by the technique.
For that reason, for example, Japanese Unexamined Patent Application Publication No. 2010-16128 suggests a technique of disposing a hydrogen supply film for supplying hydrogen to upper portions of the photoelectric conversion elements of each pixel and forming a diffusion preventing film for suppressing the diffusion of hydrogen between the hydrogen supply film and the light shielding member.
Furthermore, for example, Japanese Unexamined Patent Application Publication No. 2003-229556 suggests a technique in which the reflection preventing film is formed of material that does not contain titanium, and a barrier layer for a wiring and for a contact plug and the adhesion layer are formed of a material that does not contain titanium.
In addition, in the technique described in Japanese Unexamined Patent Application Publication No. 2010-16128, hydrogen is sufficiently supplied to the surface of the photoelectric conversion element, the gate insulation film or the like and the interface state can be terminated, and thus the dark current can be reduced.
Furthermore, it is possible to eliminate an increase in dark current noise due to an influence of titanium by the technique described in Japanese Unexamined Patent Application Publication No. 2003-229556.